Type: Prelims Only

The rare green comet that last came to Earth about 50,000 years ago has returned to the skies of Earth. C/2022 E3 (ZTF) can be seen with the naked eye if the conditions in the sky are just right.

What are Comets?

• Comets are frozen rocky or gas-filled objects that are remnants of the formation of the solar system.
• Due to their composition, characteristics and the path they move in, they tend to leave a light “behind them”.
• Here, the comet itself is green (called the head of the comet) and emits a whitish light behind it (often called the tail of the comet).
• Just like other bodies in space, comets also have orbits.
• They are sometimes pulled in close to the sun because of the sun’s gravity acting on them.
• As they orbit near the Sun, they heat up and spew gases and dust into a glowing head that can be larger than a planet.
• The remains of dust following this burning up, from a distance, look like a trail of light to humans on Earth.

What is Green Comet C/2022 E3 (ZTF)?

• Comet C/2022 E3 (ZTF) was first discovered in March last year by the wide-field survey camera at the Zwicky Transient Facility when it was already inside the orbit of Jupiter.
• While it was initially believed to be an asteroid, it began developing a tail as the Sun’s influence began vapourising the ice.
• At the time of its discovery, it was shining with a magnitude of 17.3.

Why is it green in colour?

• Comets have often been seen giving out blue or whitish light, or even green.
• In this case, the green glow “is thought to arise from the presence of diatomic carbon – pairs of carbon atoms that are bound together – in the head of the comet.
• The molecule emits green light when excited by the ultraviolet rays in solar radiation.

When and where can the green comet be seen?

• Observers in the Northern Hemisphere will find the comet in the morning sky, as it moves swiftly toward the northwest during January.
• It’ll become visible in the Southern Hemisphere in early February.
• In Indian skies, when looking in the northwest direction, one might spot it 16° above the horizon in the Bootes constellation.
• But with lights from buildings and streetlights on, it can be difficult to make it out without equipment.

Is the green comet rare?      

• It last came in the skies above Earth during the Upper Paleolithic period, a time when Neanderthals roamed the planet and early homo sapiens had just come around.
• Coming under the category of long-period comets, which take more than 200 years to orbit the Sun, the green comet is not easily spotted.
• With a highly elliptical orbit, the comet will head back to the Oort cloud and make its next appearance roughly 50,000 years later.
• But given their orbits, it’s not unique for comets to reappear close to Earth only after many, many years.

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